An impurity may be defined as any substance in the product that is neither the chemical entity defined as the drug nor an excipient [44]. Impurity
profiling is required as part of the registration process by many regulatory authorities, including the FDA and the European Union's Committee for
Medicinal Products for Human Use (CHMP). Impurities fall into one of three categories – organic substances, inorganic substances and residual
solvents [45] – and may include starting materials, intermediate compounds, reagents and catalysts, heavy metals, degradation products,
polymorphic forms (alternative crystal forms with potentially different dissolution profiles) and enantiomeric impurities, as well as
extraneous contaminants.
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